It is frequently necessary to ensure that electrical equipment cannot be operated, e.g., while maintenance work is being carried out. It is essential to ensure that circuit breakers associated with the equipment are secured in the “off” position, to protect against inadvertent operation of the breaker that could injure personnel or damage the equipment. A variety of methods have been used to secure the operating handles of circuit breakers in the “off” position, such as by locking a cabinet within which the circuit breakers are housed, or providing a locking tab mounted within a recess of a multi-pole circuit breaker housing. However, such locking tabs can be difficult to operate, and may be suitable only for multi-pole devices. It is also known to provide a locking attachment that may be screwed onto the circuit breaker housing. However, such locking attachments may require disconnection of the circuit breaker from the circuit before they can be mounted.